Armenia, a republic in western Asia, is one of the several countries that now comprise the area known as the Caucasus region and is bordered by Turkey, Iran, Azerbaijan and Georgia. It occupies part of the isthmus between the Black and Caspian seas. The country’s history can be traced back as far as the first millennium BC. Armenia prides itself on being the first nation to formally adopt Christianity in the early fourth century. Over the centuries, the Roman, Byzantine, Arab, Persian and Ottoman Empires ruled Armenia before the area was incorporated into the USSR in 1920. The most ethnically homogeneous of the fifteen republics that made up the USSR, Armenia is known for its long history of reform and political and cultural self-determination. Armenia continues to be plagued by an unresolved conflict with Muslim Azerbaijan over the primarily Armenian-populated region of Nagorno-Karabakh. Although a cease-fire has been in effect since May 1994, the economies of both sides have been hurt by their inability to make substantial progress toward a peaceful resolution.